Once in a Blue Moon is a multimedia planetarium show that answers many of the common questions that children ask about the Moon, including . . . How big and far away is the Moon? Why does the Moon seem to follow you? Where did the Moon come from? What causes the different shapes of the Moon? What is a Blue Moon?

The program is told through the story of a little girl named J.C. and her cat Whiskers, who are camping out under the stars. As J.C. falls asleep, she hears the Moon (in a female voice) call out her name. Surprised by hearing the Moon talk, J.C. is told that the Moon can only be heard speaking "once in a Blue Moon." The Moon then asks J.C. what she would like to know about the Moon. The little girl's questions form much of the remaining show.

J.C. first asks how big and how far away the Moon is. The Moon explains that if the Earth could be shrunk down 50 million times to the size of a basketball, the Moon would be the size of a tennis ball. On that same shrunk-down scale, the Earth-Moon distance would be 25 feet.

J.C. then asks why the Moon always follows her around. The Moon replies that because of her great distance from the Earth, the Moon only seems to follow people around. In reality, the Moon follows the entire Earth, and is held in place by the force of gravity.

Still on the subject of gravity, J.C. tells the Moon that she has heard that gravity is less on the Moon than it is on Earth. The Moon confirms this fact and goes on to explain that the Moon has only 1/6th the gravity of Earth, so a person who weighs 60 lbs. on the Earth would weight only 10 lbs. on the Moon. With less gravity, you'd be able to jump farther on the Moon than you can on Earth.

J.C. turns to her cat Whiskers and tells him that with less gravity, he'd have an easier time catching the mice on the Moon who are eating all the green cheese. Overhearing her remark, the Moon explains that she is not made of cheese, nor are there any mice (or any other life) on the Moon. Instead, the Moon is made of rock and dust, with no water to drink nor air to breathe.

J.C. next asks where the Moon came from. Her question is answered two ways – by a West African mythical story of the Moon's origins, followed by science's best answer to the same question. In the latter answer, the Moon explains that scientists believe that a Mars-sized planet struck the Earth very early in its history, causing a large chunk of our planet to be torn out and flung into space. For a while, this material formed a ring around the Earth, but in time, this ring of material came together to form what would become the orbiting Moon.

J.C. next asks why the Moon has dark spots on its surface. The Moon explains that the dark spots are called "maria" (pronounced MAR' EE A), a word that means seas. Early observers, she explained, thought these dark patches were seas, but with the invention of the telescope, this was disproven. A mythical story, describing a Mighty Blacksmith who made all things in the sky, explains the Moon's dark patches. Today, we know that the bright areas, which are called highlands, contain mountains and craters. We also know that the dark areas (or maria) are actually flat areas created when molten lava broke forth onto the Moon's surface long, long ago.

J.C.'s next question involves the phases of the Moon. The Moon explains that she orbits the Earth every 30 days, which defines the month (shortened from "moonth"). The underlying cause of phases is first described by a myth involving two sisters – the Sun and the Moon – and the movement of the Heavenly Bear, which changes the appearance of the Moon’s face. Next, Moon phases are explained scientifically by using a flashlight (representing the Sun), a ball (representing the Moon), and J.C. herself (representing our vantage point from the Earth). As the Moon circles the Earth, eight stages (i.e. phases) of the Moon's circular path are described in turn – the Waxing Crescent phase, the First Quarter, the Waxing Gibbous, the Full Moon, the Waning Gibbous, the Last Quarter, the Waning Crescent, and the New Moon. J.C. then recites a poem that she wrote to describe the Moon's changing phases – "First you grow face right and wax until we see you at your max. Then you shrink face left and wane and disappear when New again."

The Moon recalls that in the 1950s and 1960s, numerous objects were hurled in her direction from Earth. Some spacecraft merely flew by, while others crashed onto her surface and still others gently landed. Although there is no such thing as the "Man in the Moon," there have been men on the Moon –- 12, in fact. The first lunar landing was Apollo 11. Images and audio from that mission’s landing, first footsteps, and the reading of its inscribed plaque are next presented.

J.C.'s final question involves the Moon's earlier reference to the rarity of a "Blue Moon." As the Moon explains, a "Blue Moon" is simply the second Full Moon in the same month, which happens approximately every 2½ years. The Moon reminds J.C. that only during the "Blue Moon" can her voice be heard. Shortly thereafter, J.C. awakens from her sleep, with Whiskers still beside her.